Analysis of the failure mechanism of ZnO varistors influenced by high-resistance media based on multi-field coupling simulation

This study focuses on the distribution of high-resistance media (pores and spinels) within $\text{ZnO}$ varistors and explores the mechanical and electrical failure mechanisms of varistors under different pulse actions. Micro-CT technology revealed that the proportion of high-resistance media in the edge area is much higher than in the internal area. Simulation results indicated that a high porosity significantly increased temperature rise and thermal stress concentration, while a high spinel proportion exacerbated current concentration but had a relatively minor impact on the distribution of temperature rise and thermal stress. Under an electric field of 1000–1250 V/mm, pores transition from an insulating state to a conductive state, especially in the edge area, leading to concentrated temperature rise and thermal stress. Once the thermal stress exceeded the critical value of the mechanical strength of the pores, cracking failure occurred. The high spinel proportion in the edge area further intensified current concentration under high electric fields, working together with the conductivity of the pores to produce a significant local temperature rise, melting grain structure, and ultimately leading to puncture failure. This study provides a new perspective for understanding the failure mechanism of $\text{ZnO}$ varistors and lays a theoretical foundation for the development of varistor materials with high energy absorption capacity.